A
tangent line of a circle is any line that intersects the circle in ONLY
one point. These lines "just touch" the circle without traveling
inside. A line that intersects a circle through two points is a secant
line. Chords of circles lie on secant lines.

The
precise statement of this conjecture is:

Tangent
Conjecture I:
Any tangent line to a circle is perpendicular to the radius drawn to
the point of tangency. (top picture)